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Blue-Winged Olive (Baetis spp.)
Mayfly, hatching March–May and September–November, active in water between 38 and 58°F, and imitated at #16–22. Recorded from every region this map covers, across Michigan, Wisconsin, Virginia, North Carolina and Minnesota.
The broadest name in the box: a family of small olive-bodied mayflies with dusky blue-grey wings, Baetis and its relatives, running size 16 down to 22 with the smallest coming off in the coldest weather. Two broods a year account for the peak months of March, April and May and again September, October and November, and the working temperature band is 38 to 58 degrees — cold and cold-transitional water. The nymph is slim and fast-swimming, olive to brown, at home in almost any current, present year-round and the reason a small pheasant-tail is never wrong. Grey, drizzling days are the days; emergence is slow and film-bound, and a trailing-shuck emerger outfishes the dun most of the time. The dun itself rides a long way in cold water because it cannot get airborne quickly. The spinners are small and rusty and often fall in the morning, reversing the usual mayfly clock.
- #16–22Hook size
- 38–58°FWater, active
- Mar–May · Sep–NovPeak months
- 4Life stages fished
What it is
Mayfly · Baetis spp. · nymph → emerger → dun → spinner
The broadest name in the box: a family of small olive-bodied mayflies with dusky blue-grey wings, from Baetis and its relatives. Sizes run 16 down to 22 and the smallest come off in the coldest weather.
Two broods a year, spring and fall, and the worse the weather the better the hatch. Grey, drizzling, 45°F is the day.
When it hatches
The months below are this site's shared calendar, which covers 8 regions at once. In southeast Minnesota the state's own source says March–May and September–October, and the Minnesota page is built on that instead.
Peak is March–May and September–November. The pale months either side are the shoulder — the app widens a peak by one month in each direction and recommends the bug there, and no further: that widening is bounded so that a bug peaking in May is never offered in August.
peak shoulder not recommended
Water conditions
The band is a water temperature, not an air temperature, and it is the range in which this insect is worth fishing — for a mayfly that is the emergence window; for a scud or a midge it is simply the range trout will still eat one in.
Active from 38°F to 58°F. On this map that is cold, cold-transitional water — the band crosses 1 of the three break the river colours use. Breaks at 58, 64 and 70°F.
Stages
What the insect is doing, and what that means for what you tie on.
| Stage | What it is |
|---|---|
| nymph | A slim, fast-swimming nymph, olive to brown, at home in almost any current. It is present year-round and is the reason a small pheasant-tail is never wrong. |
| emerger | Cold, grey, drizzling days are BWO days, and the emergence is slow and film-bound. A trailing-shuck emerger outfishes the dun most of the time. |
| dun | Small olive body, upright grey wings, riding the surface a long way in cold water because it cannot get airborne quickly. |
| spinner | Small rusty spinners, often falling in the morning rather than the evening — one of the few mayflies that reverses the usual clock. |
Matching flies
8 patterns in this book imitate the Blue-Winged Olive, across its stages. Which one to tie on follows the stage the water temperature says it is in — the app makes that call on a live reading; this page lists the whole set.
- BWO Comparadun emerger · #18–22 — Flush-floating. Baetis emerge in the film and the fish know it.
- Parachute BWO dry fly · #16–22 — Olive body, grey post. The fly for a cold grey day in April or October.
- Higa's SOS nymph · #16–20 — Small, slim, and deadly in clear low water.
- Parachute Adams dry fly · #12–20 — Universal mayfly dun imitation. Every angler carries these.
- Perdigon nymph · #14–20 — Slim, epoxied, sinks like a stone. The euro-nymphing point fly.
- Pheasant Tail Nymph nymph · #12–22 — The mayfly nymph. Beadhead or not, size 16, and half the trout in the world have eaten one.
- RS2 emerger · #16–24 — The emerger that saves a hatch you cannot otherwise crack. Fish it in the film.
- Zebra Midge nymph · #18–24 — Two materials and a bead. The winter fly, and the fly for the last two feet of a tailout.
Where to find it right now
The rivers with a page here that sit in this insect's regions, with a USGS gauge reporting water temperature. This list is re-ranked against the reading each gauge is sending now and today's date, so it is live — the fallback below it, if the readings do not arrive, is each river's measured July mean.
- Ararat River the North Carolina mountains · July mean 49.9°F
- Back Creek the Virginia mountains · July mean 49.9°F
- Big Cherry Creek the Virginia mountains · July mean 49.9°F
- Big Ivy Creek the Virginia mountains · July mean 49.9°F
- Boothe Creek the Virginia mountains · July mean 49.9°F
- Brogan Branch the Virginia mountains · July mean 49.9°F
- Browns Dan River the Virginia mountains · July mean 49.9°F
- Brushy Fork the Virginia mountains · July mean 49.9°F
- Camp Creek the Virginia mountains · July mean 49.9°F
- Conners Creek the Virginia mountains · July mean 49.9°F
Regional presence
Regions, not collection records. This insect is recorded from the coarse regions below; nobody has surveyed which named river it has been caught on, and this page will not pretend otherwise.
- northern lower Michigan MI
- southern lower Michigan MI
- the Upper Peninsula MI
- the Wisconsin driftless WI
- northern Wisconsin WI
- the Virginia mountains VA
- the North Carolina mountains NC
- southeast Minnesota MN
Rivers in these regions with a page here
- Au Sable River
- Catawba River
- Jackson River
- Muskegon River
- Escanaba River
- Saint Croix River
- Smith River
- Tygart Valley River
- Kalamazoo River
- Aaron Creek
- Aaron Run
- Aarons Run
- Abb Run
- Abes Run
- Abitosse Creek
- Abram Creek
- Acme Creek
- Acorn Branch
- Adamcamp Branch
- Adams Creek
- Adams Creek
- Adamson Run
- Addis Creek
- Adkins Rockhouse Branch
- and 6470 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Hendrickson Ephemerella subvaria · Mayfly · April–May
- Blue Quill Paraleptophlebia adoptiva · Mayfly · April–May
- Mahogany Dun Paraleptophlebia spp. · Mayfly · September–October
- Light Cahill Maccaffertium ithaca · Mayfly · May–July
- Sulphur Ephemerella invaria · Mayfly · May–July